1、
1/6×2/3÷(4/5-8/15)
=1/6×2/3÷(12/15-8/15)
=1/6×2/3÷4/15
=1/6×2/3×15/4
=1/9×15/4
=5/12
2、
1/6+3/4×2/3÷2
=1/6+3/4×1/3
=1/6+1/4
=2/12+3/12
=5/12
3、
(1/2-3/8)÷(1-1/4)
=(4/8-3/8)÷3/4
=1/8×4/3
=2/3
4、
7/9÷11/5+2/9×5/11
=7/9×5/11+2/9×5/11
=(7/9+2/9)×5/11
=1×5/11
=5/11